1. Field of the Invention
The present invention relates to a planar light-emitting device that illuminates a liquid crystal display panel or the like. The present invention also relates to a liquid crystal display apparatus using such a planar light-emitting device.
2. Description of Related Art
Liquid crystal display apparatuses are widely used as the large-sized displays of flat-screen televisions and monitors, etc. These liquid crystal display apparatuses employ a backlight unit that applies illuminating light to a liquid crystal display panel from the back or the lower side of the liquid crystal display panel to enhance the luminance of the display screen.
The backlight unit has a lightguide plate and a light source comprising, for example, a plurality of light-emitting diodes (LEDs) disposed along one side edge surface of the lightguide plate. The lightguide plate receives light from the LED light source, guides the light through the lightguide plate and emits the guided light from the whole light-exiting surface of the lightguide plate toward a liquid crystal display panel.
Recently, as liquid crystal televisions increase in size, backlight units used therein have been demanded to further reduce in weight and thickness. In this regard, there have been some problems to be solved. As the thickness of a lightguide plate constituting a backlight unit is reduced, it becomes likely that color irregularity and luminance unevenness will occur in light emitted from the lightguide plate. If injection molding is employed as a method of producing a large-sized lightguide plate, it is difficult to fill the resin material throughout the molding tool for the large lightguide plate. Increasing the injection pressure can solve this problem, which, however, causes an increase in installation cost. Extrusion molding can produce large-sized and thin lightguide plates but cannot appropriately form microscopic optical configurations on the lightguide plates.
Meanwhile, there have been developed planar light-emitting devices in which a plurality of lightguide plates are arranged side by side with their respective upper surfaces as light exiting-surfaces being flush with each other and a plurality of light sources are provided in association with the lightguide plates to obtain a wide light-exiting surface (see Japanese Patent Application Publication Nos. Hei 9-186825 and Hei 11-288611).
In the planar light-emitting devices disclosed in the above-described Japanese Patent Application Publications, however, a plurality of light sources and lightguide plates are each placed directly in a frame or on a board when these components are mounted. Therefore, it is difficult to accurately position each lightguide plate with respect to the optical axis of the corresponding light source. In addition, it is difficult or may be impossible to replace only one or more lightguide plates suffering from luminance unevenness or other problem.